The invention relates to a wiring line structure and, more particularly, to a wiring line structure on a transparent substrate and a method for fabricating the same, improving film coverage and simplifying process steps.
A typical liquid crystal display (LCD) includes a thin film transistor (TFT) substrate, a color filter (CF) substrate, and a liquid crystal layer disposed therebetween. The TFT substrate contains a plurality of matrix pixels consisting of a plurality of data lines and a plurality of scan lines, and a plurality of pixel driving circuits consisting of a plurality of electric devices, such as thin film transistors and capacitors. Traditionally, the line material (data line or scan line) for connecting to the transistors comprises Al, Cr, Mo, or W, wherein Al material with higher electric conductivity is commonly used as a gate line (scan line). However, increased size and resolution of LCDs requires reducing resistance-capacitance RC delay. Accordingly, there has been an increase in the use of copper with good electric conductivity as a wiring line material for LCD devices rather than aluminum.
It is, however, very difficult to etch a copper layer and to control the taper angle of the copper wiring line, resulting in reduction of film coverage in the subsequent deposition. Moreover, copper easily reacts with silicon, forming copper silicide (i.e. Cu3Si), reducing device performance. Additionally, copper atoms easily diffuse in the silicon oxide, increasing current leakage. Moreover, the copper layer has poor adhesion strength with the underlying glass substrate. Accordingly, if copper is used as a wiring line material, the fabrication of LCD devices may become more difficult, reducing device performance and reliability.